The present invention relates to a substrate processing method and apparatus for use in removing a coating film (a photoresist film and an anti-reflective coating film) formed on a surface of an LCD (liquid crystal display) substrate or on a layer (semiconductor layer, insulating layer, electrode layer) formed on the substrate, from peripheral portion thereof.
In an LCD manufacturing process, a photolithographic technology is usually employed similarly in a manufacturing process for a semiconductor device. In the photolithographic process for LCD, a resist coating film is first formed on a glass substrate. The resultant substrate is pattern-exposed and developed. Thereafter, a semiconductor layer, an insulating layer, and an electrode layer formed on the substrate are selectively etched to obtain an ITO (Indium Tin Oxide) thin film and an electrode pattern.
When a resist solution is applied onto the LCD substrate, it forms a film. Although it is uniform in thickness immediately after the coating, the resist solution rises up at the peripheral portion of the substrate by the influence of the surface tension after rotation is terminated and centrifugal force is no longer applied to the substrate, or with the passage of time. Furthermore, the resist solution spreads and reaches a lower peripheral portion of the substrate G to form an undesirable film. When the non-uniform film (thick in the periphery of the substrate G) is thus formed, the peripheral resist film is not completely removed and left even at the time an integrated circuit pattern is developed. The remaining resist will be removed during the step of transporting the substrate G, leading into particles.
Then, after the resist solution is applied onto the substrate G, the substrate G is transported to a peripheral resist removing mechanism to remove the resist coating film from the peripheral portion of the substrate G. Such a resist removing mechanism is disclosed in U.S. Pat. Nos. 5,718,763 and 5,695,817.
In the meantime, to dissolve the resist solution, a solvent such as n-butyl acetate (NBA) or methylethyl ketone (MEK) has been conventionally used. However, a large amount of the solvent leaks out into the working atmosphere in a factory for producing the LCD substrate in quantity. Under the circumstances, a so-called "safe solvent" having little negative effect on a human body, has been increasingly used. As an example of the safe solvent, an organic solvent such as OK73 thinner (manufactured by TOKYO OHKA KOGYO CO., LTD) may be used. OK73 thinner contains propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) in a ratio of 3:7. As another example, 2-heptanon may be mentioned. 2-heptanon is a less-volatile solvent having a high boiling point (e.g., 140.degree. C. or more).
Of these safe solvents, however, OK 73 thinner has a poorer solubility of the resist film than conventionally employed solvents. It is therefore difficult to remove the resist coating film completely from the peripheral portion of the substrate by a method employing the conventionally-employed solvent.